1. Field of the Invention
The present invention relates to an improvement in an electromagnetic actuator comprising: a stationary core supported on a bottom wall of a housing made of a magnetic material; a movable core opposed to the stationary core with an air gap left therebetween to drive a movable member; a coil assembly constructed by winding a coil around a bobbin which is supported in the housing and surrounds the stationary and movable cores; and a tubular bearing member which is disposed inside the coil assembly and slidably supports the movable core on its inner peripheral surface.
2. Description of the Related Art Japanese Patent Application Laid-open No. 2001-1765 discloses a conventional electromagnetic actuator.
In the conventional electromagnetic actuator, the bearing member is formed into a bottomed cylindrical shape, and a set spring is mounted under compression between a bottom of the bearing member and the movable core so that the set spring retains the bottom of the bearing member on a support portion formed on the housing while being in abutment against the support portion.
The present inventors discovered that wear powder is generated between the set spring and a portion on which the set spring is pressed by slight movement of the set spring within the bearing member, and the wear powder may enter sliding portions of the bearing member and the movable core, to deteriorate the sliding of the movable core. The resilient force of the set spring is also applied to the movable core in a direction to draw it away from the stationary core, and hence an effective attraction force generated between the stationary and movable cores is reduced by an amount corresponding to the resilient force.